From moving states, terminals may be divided into two types. One type refers to terminals at fixed positions, such as home terminals; and the other type refers to terminals in a moving state, e.g., mobile terminals which are easily carried, such as mobile phones, Personal Digital Assistants PDAs and so on. Herein, when a home terminal accesses the Internet, an effective Internet Protocol IP address needs to be applied from the Internet. The IP address has dual identities, and it not only represents the identity of the home terminal, but also represents a network topology location of the home terminal. In other words, for a terminal at a fixed position, the IP address applied from the Internet can identify the dual identities of the terminal.
For a mobile terminal (a mobile user), by taking a mobile terminal A as an example, when the mobile terminal A moves from a control area of one access gateway to a control area of another access gateway, i.e., from one network topology location to another network topology location, the mobile terminal A needs to acquire a corresponding IP address in each of different control areas, and thus can successfully access the network.
In consideration of the shortage in IP address resources, operators change the mode of allocating IP addresses to mobile users. Further, the original mode that public network IP addresses are directly allocated to the mobile users is changed to a mode that firstly private network IP addresses are allocated to the mobile users and then the private network IP addresses are translated into the public network IP addresses through a pre-deployed operation-level Network Address Translation NAT device to save the IP address resources when the mobile users accesses the Internet.
However, since a mobile user is usually in a moving state and may be accessed the network through different access devices or different operation-level NAT devices, consequently, when the mobile terminal is accessed the Internet, private network IP addresses allocated thereto and translated public network IP addresses are different. This causes the following problems to operators and service providers:
for the operators, each mobile terminal in the network is accessed the network by using different IP addresses, such that the search for illegal operation terminals cannot be realized, i.e., the tracing to the terminal cannot be realized, and further the network security cannot be guaranteed. For the service providers, since network access addresses of the same mobile terminal change ceaselessly, effective tracking and service access analysis cannot be performed on the mobile terminal, and further better service cannot be provided for the mobile terminal.